The putative role of the vomeronasal chemosensory system is to receive species-specific odors such as pheromones. In fact, its central connections project to brain structures involved in reproduction. However, so far, little is known about its information processing mechanisms. The long term goal of this project is to contribute to our understanding of the morphological pattern of the accessory olfactory bulb to better clarify its working mechanisms. Our program intends to characterize the types of neurons of the accessory olfactory bulb by describing their morphology, synaptology and immunocytochemical characteristics, and to examine if there are some anatomical and/or chemical correction(s) between these neurons and the secondary brain centers of the vomeronasal system. To achieve this goal, the morphology and the synaptology of the neurons of the accessory olfactory bulb will be studied by light- and electron-microscopic procedures. Specific relevant antigens will be localized with appropriate immunocytochemical methods. Direct correlation between the morphology and the chemical characteristics will be achieved by double staining of the same neurons by immunocytochemical and Golgi procedures. Furthermore, the tracing methods will be used to determine the projection areas of output neurons of the accessory olfactory bulb. This project will help in our understanding of the olfactory sensory mechanisms and consequently disorders of the olfactory system.